Module: ActiveRecord::AttributeMethods::Serialization::ClassMethods

Defined in:
activerecord/lib/active_record/attribute_methods/serialization.rb

Instance Method Summary collapse

Instance Method Details

#serialize(attr_name, class_name_or_coder = Object, **options) ⇒ Object

If you have an attribute that needs to be saved to the database as a serialized object, and retrieved by deserializing into the same object, then specify the name of that attribute using this method and serialization will be handled automatically.

The serialization format may be YAML, JSON, or any custom format using a custom coder class.

Keep in mind that database adapters handle certain serialization tasks for you. For instance: json and jsonb types in PostgreSQL will be converted between JSON object/array syntax and Ruby Hash or Array objects transparently. There is no need to use #serialize in this case.

For more complex cases, such as conversion to or from your application domain objects, consider using the ActiveRecord::Attributes API.

Parameters

  • attr_name - The name of the attribute to serialize.

  • class_name_or_coder - Optional. May be one of the following:

    • default - The attribute value will be serialized as YAML. The attribute value must respond to to_yaml.

    • Array - The attribute value will be serialized as YAML, but an empty Array will be serialized as NULL. The attribute value must be an Array.

    • Hash - The attribute value will be serialized as YAML, but an empty Hash will be serialized as NULL. The attribute value must be a Hash.

    • JSON - The attribute value will be serialized as JSON. The attribute value must respond to to_json.

    • custom coder - The attribute value will be serialized using the coder's dump(value) method, and will be deserialized using the coder's load(string) method. The dump method may return nil to serialize the value as NULL.

Options

  • :default - The default value to use when no value is provided. If this option is not passed, the previous default value (if any) will be used. Otherwise, the default will be nil.

Examples

Serialize the preferences attribute using YAML
class User < ActiveRecord::Base
  serialize :preferences
end
Serialize the preferences attribute using JSON
class User < ActiveRecord::Base
  serialize :preferences, JSON
end
Serialize the preferences Hash using YAML
class User < ActiveRecord::Base
  serialize :preferences, Hash
end
Serialize the preferences attribute using a custom coder
class Rot13JSON
  def self.rot13(string)
    string.tr("a-zA-Z", "n-za-mN-ZA-M")
  end

  # Serializes an attribute value to a string that will be stored in the database.
  def self.dump(value)
    rot13(ActiveSupport::JSON.dump(value))
  end

  # Deserializes a string from the database to an attribute value.
  def self.load(string)
    ActiveSupport::JSON.load(rot13(string))
  end
end

class User < ActiveRecord::Base
  serialize :preferences, Rot13JSON
end

103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
# File 'activerecord/lib/active_record/attribute_methods/serialization.rb', line 103

def serialize(attr_name, class_name_or_coder = Object, **options)
  # When ::JSON is used, force it to go through the Active Support JSON encoder
  # to ensure special objects (e.g. Active Record models) are dumped correctly
  # using the #as_json hook.
  coder = if class_name_or_coder == ::JSON
    Coders::JSON
  elsif [:load, :dump].all? { |x| class_name_or_coder.respond_to?(x) }
    class_name_or_coder
  else
    Coders::YAMLColumn.new(attr_name, class_name_or_coder)
  end

  attribute(attr_name, **options) do |cast_type|
    if type_incompatible_with_serialize?(cast_type, class_name_or_coder)
      raise ColumnNotSerializableError.new(attr_name, cast_type)
    end

    cast_type = cast_type.subtype if Type::Serialized === cast_type
    Type::Serialized.new(cast_type, coder)
  end
end